Electronic converters for light sources comprising, for example, at least one light-emitting-diode (LED) or other solid-state lighting means, such as for example laser diodes, can supply a d.c. current at output.
FIG. 1 shows a possible lighting system comprising an electronic converter 10 and at least one lighting module 20. For instance, illustrated in FIG. 1 are two lighting modules 20a and 20b that are connected in parallel.
In general, each lighting module 20 can be incorporated with the electronic converter 10 in an integrated lighting system or can be connected through cables to the electronic converter 10.
The electronic converter 10 usually comprises a control circuit 102 and a power circuit 12 (for example, an AC/DC or DC/DC switching power supply), which receives at input a supply signal (for example, from the electric-power line) and supplies at output a d.c. current via a power output 106. This current may be stable or even vary over time, for example, in order to regulate the intensity of the light emitted by the lighting modules (the so-called “dimming” function). For instance, the control circuit 102 can set via a reference channel Iref of the power circuit 12 the current required by the LED module or modules 20.
In general, regulation of the intensity of light emitted by the lighting module 20 can be achieved by regulating the average current that traverses the lighting module 20, for example by setting a lower reference current Iref, or by activating and deactivating the power output 106, for example through a pulse-width-modulation (PWM) signal.
In general, a LED module 20 can comprises a single LED or a plurality of LEDs. For instance, FIG. 2 shows an example in which the lighting module 20 comprises a LED chain (or LED string), in which a plurality of LEDs is connected in series.
Furthermore, the LEDs may also be divided on different branches connected in parallel. For instance, each module 20 could comprise a plurality of LED strings connected in parallel.
The LED strings may differ from one another for different factors, for example in relation to the number and type of LEDs, the operating temperature or other parameters such as to enable the voltage across one string to be different from the voltage across the string or strings. For this reason, the solution illustrated in FIG. 1 of connecting the strings directly together in parallel is frequently not practicable in so far as the electric power supply is distributed in an uncontrolled way over the various strings.
FIGS. 3 and 4 illustrate various solutions that may be used for ensuring a better uniformity of the distribution of the power over a number of lighting modules 20.
For instance, FIG. 3 shows an example where each lighting module 20 is supplied via an additional electronic converter 30. In particular, in the example considered three lighting modules 20a, 20b and 20c are illustrated, which are supplied via three additional current generators 30a, 30b and 30c, such as for example buck converters. For instance, these current generators 30a, 30b and 30c may be connected in parallel to the line 106, and the electronic converter 10 could set up a constant voltage on the line 106.
Instead, FIG. 4 shows an example where each lighting module 20a, 20b and 20c is connected in series to a respective current regulator 40a, 40b and 40c, such as for example a linear current regulator, and the lighting modules 20a, 20b and 20c are supplied via a common voltage. This voltage could also be regulated on the minimum value possible determined, for example, through sensors that detect the dropout voltage on the linear regulators.
Instead of the current regulators 40a, 40b and 40c also current mirrors or a transformer with a number of secondary windings may be used.
In this case, the dimming function could be performed also via the aforesaid current regulators 40a, 40b and 40c, for example:
a) by selectively activating or deactivating the respective current regulator 40a, 40b and 40c via a driving signal, such as for example a PWM signal; or
b) in the case where adjustable current regulators are used, by setting the reference current of the current regulators 40a, 40b and 40c. 
In general, the current generators 30a, 30b and 30b or the current regulators 40a, 40b and 40c may also be incorporated in the respective lighting modules 20a, 20b and 20c. 
Furthermore, the light sources L of each branch may also be divided over a number of lighting modules that are connected in series, i.e., a plurality of lighting modules connected in series could be used instead of each lighting module 20a, 20b and 20c illustrated in FIGS. 1 to 4.
Typically the lighting modules 20 can be exchanged even by non-specialized persons, and consequently the lighting modules 20 and the converter 10 have to be protected from electrostatic discharge.
For instance, FIG. 5 shows an example of a typical protection circuit, where each lighting module 20 comprises a Zener diode DESD connected in antiparallel with the respective LED string L. In general, a respective Zener diode DESD could be provided for each LED or subset of LEDs of the string. In fact, typically, a protection diode is provided for each unit or subset of LEDs that has electrical contacts that are accessible.
The person skilled in the art will appreciate that, instead of a Zener diode, a transient-voltage-suppression (TVS) diode could also be used.
In general, such protection diodes can be provided directly inside the packages of the light sources L, or on the printed circuit of the lighting module 20.
For instance, FIG. 6 shows an example of a known protection circuit for a LED string.
In the example considered, the LED string comprises a plurality of LEDs, for example four LEDs L1, L2, L3 and L4, which can be connected to an electronic converter 10.
In the example considered, a respective protection diode is connected in antiparallel to each LED L, and consequently the protection circuit 30 comprises four diodes DESD1, DESD2, DESD3 and DESD4, such as for example Zener diodes.
In addition, a further diode DARB may be provided, such as for example a Schottky diode, which is connected in series to the LED strings, for example between the positive terminal 106 of the converter 10 and the LED string, in such a way as to protect the LED string from reverse biasing.
Evidently, the aforesaid protection diodes add further costs and in the case where the LED strings are not protected mechanically, for example via a resin or silicone, a protection diode should be provided for each LED.